1. Field of the Invention
The invention relates to a two-pole motor""s stator for a household fan, and more particularly, to an improved motor""s stator design with less stator""s iron loss, reduced temperature rise, more torsion output and greater rotation efficiency.
2. Description of the Related Art
Conventional household fans (e.g. electric fans, extractor fans, exhaust blowers, etc.) employ a squirrel-cage rotor""s motor as power source. Depending upon the revolutions and torsion, the squirrel-cage rotor""s motor has two-pole or four-pole configuration. Generally speaking, the output torsion of common motors is proportional to the square of the outer diameter of their rotors. Under this precondition that the stator""s area remains unchanged, the increase of the rotor""s diameter must lead to an increase of the diameter of the rotor-receiving middle hole of the stator, thereby reducing the height of stator""s yoke (range of effective diameter from the outermost point of each slot to the stator""s rim). Accordingly, the yoke magnetic density is so increased that it can""t match with tooth magnetic density of the stator. In addition, the stator""s iron loss and the temperature rise are also increased and the operational efficiency is lowered. In order to gain a balance point among the iron loss, efficiency and output torsion, it""s inevitable to give up partial output torsion for achieving the increase of the efficiency. Accordingly, how to effectively upgrade the rotor""s output under the restriction of fixed stator""s area becomes a problem that experts in this field tries to overcome.
As shown in FIG. 1, a conventional two-pole stator 40 is formed by stacking up a plurality of silicon steel sheets 4. Meanwhile, the silicon steel sheets 4 include a middle hole 31 for receiving a rotor 6. A plurality of slots 42, around which a coil 5 is wound, is provided along the circumference of the middle hole 31. After the stator 40 and the rotor 6 are assembled (see FIG. 2), the slot 42 is through a slot neck 421 in connection with the middle hole 41, and the slot neck 421 is formed with two side rims 422 extending radially outwardly. A rounded corner 423 is formed between each side rim 422 and a straight end rim 424. The rotor 6 is received within the middle hole 41 of the silicon steel sheets 4 and kept at a certain clearance to the rim of the middle hole 41. After the current flows through the coil 5, a magnetic field is created to bring the rotor 6 into rotation. At the same time, the fan""s blades are revolved.
The above-mentioned is a commonly used rotor""s configuration of two-pole motor for household fans. In order to facilitate the assembly, the slot 42 has to reach a certain slot-occupying ratio which means the extent of the slot 42 wound by the coil 5. The greater the ratio is, the more crowded the slot 42 is, thereby leading to an inconvenient assembly. On the contrary, the smaller the ratio is, the looser the slot 42 is, thereby facilitating the assembly. In order to increase the slot""s 42 area and, therefore, to reduce the slot-occupying rate, the height of the side rims 422 has to be increased under the precondition of fixed tooth width of silicon steel sheets 1 (that is, the fixed clearance between every two slots 42). However, this results in the decrease of height of stator""s yoke (that is, range of effective diameter from the outermost point of each slot to the stator""s rim), thereby increasing the stator""s iron loss and, therefore, affecting the rotational efficiency. Accordingly, the most commonly used ratio of the diameter of the middle hole 41 of the stator and the effective outer diameter (described as xe2x80x9caxe2x80x9d in FIG. 2) is 0.52-0.55 to 1. To take an example that the effective outer diameter of the silicon steel sheets 4 is 60 mm and the diameter of the middle hole is 31.5 mm, they are in a ratio of about 1:0.525. Meanwhile, the effective outer diameter of the slots 42 is described as xe2x80x9cbxe2x80x9d in FIG. 2 at about 50 mm while the yoke height is:
(axe2x88x92b)/2.
Substitute the known values
(60xe2x88x9250)/2
And the yoke height is 5 mm. This is a result of compromise between the rotational efficiency (lower iron loss and temperature rise) and the rotation feature (higher torsion output).
It is a primary object of the invention to remove the above-mentioned drawbacks and to provide a two-pole motor""s stator for a household fan in which the stator""s middle hole of stator""s silicon steel sheets is so enlarged that each slot at the circumference of the middle hole has a greater width. Meanwhile, the slot""s height is reduced. Thus, under the precondition without reducing the slot""s area (which influences the assembling efficiency), the enlargement of the middle hole for accommodating a rotor with a greater diameter is capable of increasing the torsion output of the motor. Moreover, the increase of the yoke height is capable of reducing iron loss and temperature rise and enhancing the rotation efficiency.
It""s another object of the invention to provide a two-pole motor""s stator for a household fan having a tapered form which is so created at the close end of the slots that the slots are through corresponding slot necks in connection with the middle hole, and two sides of the slot neck are bent outwardly at an obtuse angle and then in connection with two side rims extending radially outwardly from the middle hole whereupon a rounded corner is formed between each side rim and a first end rim, and that an obtuse angle is formed by the first end rim and a second end rim of the slots. Accordingly, the height required by both side rims of the slots is effectively reduced for increasing the stator""s yoke height.